The oil pump is running but it is generating less pressure at idle.

You should however keep the revs lower, not as low as idle as you point out but also don't red line it. If it's a turbo try not to generate lots of boost either.

You are absolutely not supposed to do that. In fact, you're supposed to do the opposite. Letting your car idle to warm up kills it faster because the oil pump isn't running because the car isn't moving.

That is absolutely not true. The engine runs the oil pump, so the pump is working as long as the engine is spinning, assuming the pump is not faulty, of course. I'm not aware of any car engine ever built where that isn't true.

That being said, idling your (modern) car for longer than a minute, or as long as necessary to defrost the windows in the winter, is a waste of fuel and, consequently, emissions. It's also an unnecessary wear on mechanical parts, but not because the engine is cold or hot, but simply because it's in use.

https://www.consumerreports.org/cars/cars-driving/should-you-warm-up-your-car-before-driving-a5580016349/

The car doesn't have to be in gear for the oil pump to run. If the engine is running the oil pump is on. That's why there's a red light that looks like an oil can when the key is on before you start it but it turns off when the engine is running because there is oil pressure. If that light is on when the engine is running you need to shut it off immediately or you're going to be replacing an engine.

This is 100% correct. There's a lot of "tips and tricks" that are extremely out dated, and typically for vehicles prior to the implentation of fuel injection.